1. Field of the Invention
The present invention relates to electrical contacts, and more particularly to an electrical contact for mounting on a printed circuit board.
2. Description of the Related Art
Electrical pin contacts have been developed to provide an electrical interface between a printed circuit board and other electronic components. Electrical pin contacts can be used to establish an electrical interconnection to circuitry on a printed circuit board through a plated-through hole on the printed circuit board to which the circuitry is connected. For example, the pin contacts can provide a direct connection between two printed circuit boards, wherein each end of the contact makes an electrical connection to the printed circuit boards. As another example, a pin contact can provide an interface for an electrical connector to interconnect a printed circuit board to other electronic components.
In general, electrical pin contacts for printed circuit boards can be categorized as either a solder contact or a solderless contact. For either type of contact, it is desirable that the contact contribute to both the mechanical and electrical integrity of the joint between the contact and the printed circuit board.
For solder contacts, the solder joint itself typically contributes toward a significant portion of both the mechanical and electrical integrity between the contact and the plated-through hole on the printed circuit board. Although a solder joint can provide adequate mechanical support for the contact, the integrity of the solder joint can be compromised unless the contact is properly supported in the plated-through hole during the soldering process. In particular, as solder transforms from the liquid phase to the solid phase, it passes through a plastic phase during which time movement of the electrical contact relative to the plated-through hole can introduce fractures into the solder joint that could ultimately cause failure of the solder joint.
In an effort to improve the overall integrity of solder joints, electrical pin contacts have been developed which provide mechanical support between the contact and a plated-through hole. In addition to inhibiting movement when being soldered to the plated-through hole of the printed circuit board, these contacts can also reinforce the structure of the solder joint. However, solder contacts typically rely upon either deformation of a portion of the contact after insertion into a hole which requires additional manufacturing steps, or an interference fit which results in deformation of a substantial portion of the hole. Examples of these contacts include U.S. Pat. Nos. 3,601,750 and 5,410,452. Mancini, in the '750 patent, discloses a square pin contact having a cylindrical ferrule placed over and secured to each corner of the contact along an intermediate portion thereof. The contact is inserted into a plated-through hole on a circuit board so that the ends of the ferrule extend from each side of the circuit board. The ends of the ferrule are then deformed to engage and secure the contact to the circuit board. Sinclair et al, in the '452 patent, discloses an adapter pin having a round knurled end, which is press fit into a plated-through hole on a printed circuit board. To establish a rigid mechanical connection between the pin and the circuit board, the knurled end is configured to have a diameter which is larger than the diameter of the plated-through hole to provide an interference fit resulting in substantial deformation of the hole circumference.
For solderless pin contacts, the electrical contact itself provides both the mechanical support and electrical connection between the contact and a plated-through hole on a printed circuit board. In general, solderless contacts are press-fit into a plated-through hole to both establish an electrical connection and provide mechanical support between the contact and hole. As contact pressure between the contact and hole increases, which can result by increasing the interference between the contact and hole, electrical and support characteristics tend to improve. However, as the contact pressure increases, greater mechanical stresses are placed on the plated-through hole and fiberglass material of the printed circuit board. If the contact pressure becomes too high, the integrity of the plated-through hole can be compromised resulting in failure of the plated-through hole and the printed circuit board.
Solderless pin contacts that have been developed typically include a compliant section to engage a plated-through hole on a circuit board. The purpose of the compliant section is to establish both an electrical connection and mechanical support between the contact and the plated-through hole by exerting sufficient contact pressure on the hole. Examples of compliant pin contacts include U.S. Pat. Nos. 4,443,053; 4,746,301; 4,758,187; 4,776,807; and 4,795,378. Each of these contacts includes a compliant section along a length of the contact having a particular cross-sectional shape which collapses or deforms when inserted into a plated-through hole to attempt to minimize hole distortion. Astbury, in the '053 patent, discloses an electrical contact that includes a compliant section formed having end sections that are slidable relative to a central section when the contact is inserted into a plated-through hole. Key, in the '301 patent, discloses a compliant pin having an S-shaped cross-section. Guglhor, in the '187 patent, discloses a contact pin having a cross-section shaped similar to an I-beam which collapses upon insertion into a plated-through hole. Trainer et al, in the '807 patent, discloses an electrical contact including a compliant section having a U-shaped cross-section which deforms upon insertion into a plated-through hole to create a positive electrical contact. Tomizu et al, in the '378 patent, discloses a terminal pin including a compliant portion having a roughly V-shaped cross-section which deforms inwardly when inserted into a plated-through hole.
Accordingly, there is a need for an electrical contact which can be press-fit into a plated-through hole on a printed circuit board to support the contact in the hole with minimal hole distortion and minimal contact pressure on the hole.
It is an object of the present invention to provide an improved electrical contact for soldering in a plated-through hole on a printed circuit board.